1. Field of the Invention
This invention relates to the preparation of isomaltulose and, more particularly, to the preparation of isomaltulose from sucrose.
2. Description of the Prior Art
Isomaltulose is an intermediate product for the preparation of glucopyranosido-1,6-mannitol (German Auslegeschrift No. 2 520 173) and glucopyranosido-1,6-sorbitol (isomaltitol, German Pat. No. 2 217 628). Both substances may be used as sugar substitutes.
German Pat. No. 1 049 800 discloses that sucrose is enzymatically converted into isomaltulose. The enzymes are of microbial origin. Besides Protaminobacter rubrum, other bacteria such as Erwinia carotovora, Serratia marcescens, Serratia plymuthica and Leuconostoc mesenteroides are capable of this rearrangement (S. Schmidt-Berg-Lorenz, W. Mauch, ZEITSCHRIFT FUER DIE ZUCKERINDUSTRIE, 14, 625-627, [1964]; F. H. Stodola, 126th Meeting of Amer. Chem. Soc., Sept., 1954, Abstracts of papers, p. 5D; W. Mauch, S. Schmidt-Berg-Lorenz, ZEITSCHRIFT FUER DIE ZUCKERINDUSTRIE, 14, 309-315 and 375-383 [1964]).
German Pat. No. 2 217 628 further discloses that the enzymatic conversion of sucrose into isomaltulose can be carried out continuously or batch-wise in a 15 to 40% solution with strong stirring and under aerobic conditions at 20.degree. to 37.degree. C.
Moreover, German Offenlegungsschrift No. 2 806 216 discloses how to carry out continuously the culture of isomaltulose-forming microorganisms with simultaneous conversion of sucrose into isomaltulose.
The above-cited known processes suffer from disadvantages, such as:
(a) the living and multiplying cultures of cells consume i.e., oxidize part of the added sucrose for their own living activity (growth and multiplication), so that this part of the sucrose is no longer available for the isomaltulose conversion;
(b) the conversion of the sucrose into isomaltulose and the simultaneous cell multiplication require fermentation with strong agitation and aeration which, in turn, cause high energy consumption;
(c) the concentration of the nutrient substrate of 25% (German Offenlegungsschrift No. 2 806 216) or of 15 to 40% (German Pat. No. 2 217 628) is insufficient for the subsequent production of isomaltulose by direct crystallization (the converted sucrose solution following separation of the cell substance must first be concentrated by evaporation before it can be subjected to crystallization; thus, from 100 kg of converted sucrose solution according to German Offenlegungsschrift No. 2 806 216, about 67 kg of water must be evaporated before isomaltulose crystallizes out);
(d) the multiplication of the cell substance requires not only a suitable carbon source, but also nitrogen salts and nutrient salts (in the above-cited process, the addition of nitrogen and nutrient salts takes place by using sugar solutions of lower purity, such as obtained in sugar mills, in lieu of pure sucrose solutions; these impurities [non-sugars], on one hand, are absolutely necessary for cell growth but, on the other hand, cause loss of isomaltulose during the crystallization due to molasses formation).
The above-cited disadvantages can be avoided in principle provided that it be possible to separate the conversion of sucrose into isomaltulose from the cell multiplication and to stabilize it over a substantial length of time.
It is an object of the present invention, therefore, to provide a continuous conversion of sucrose into isomaltulose (palatinose, 6-O-.alpha.-D-glucopyranosido-D-fructose) which avoids the disadvantages discussed above.